Reinforcement steel

ABSTRACT

A reinforcement steel bar includes a shaft part and a head part formed by forging an end portion of the shaft part. The head part is provided with a projection projecting from the shaft part in a radial direction of the shaft part, and a recess formed along a corner portion between an outer peripheral surface of the shaft part and the projection.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to reinforcement steel.

2. Description of the Related Art

A coupling structure for coupling decks laid on a bridge is configured such that a reinforcement steel bar of one of the decks and a reinforcement steel bar of the other deck are caused to project to a space between the decks, and concrete is placed in the space.

There is an example of reinforcement steel used in a ferroconcrete structure such as the aforementioned deck coupling structure, in which a diameter of a head part of the reinforcement steel is expanded more than a diameter of a shaft part thereof (see Japanese Patent Application Publication No. 2005-139650, for example).

SUMMARY OF THE INVENTION

The conventional ferroconcrete structure described above allows to increase the anchoring force to concrete against the tensile force applied in the axial direction of the reinforcement steel buried in the concrete since the head portion of the reinforcement steel is engaged with the concrete. However, the conventional ferroconcrete structure still has a problem that the fatigue resistance of the joint portion of the head portion and the axial portion is decreased since a stress is likely to be concentrated on the corner portion between the head portion and the outer peripheral surface of the axial portion when bending tensile force or punching shearing force is applied to the reinforcement steel.

An object of the present invention is to solve the aforementioned problem by providing reinforcement steel which is capable of increasing an anchoring force to concrete and enhancing the fatigue resistance of the reinforcement steel.

To solve the problem, the present invention provides reinforcement steel which includes a shaft part and a head part formed by forging an end portion of the shaft part. The head part is provided with a projection projecting from the shaft part in a radial direction of the shaft part, and a recess formed along a corner portion between the outer peripheral surface of the shaft part and the projection.

According to the present invention, when a stress attributable to a bending tensile force and to a punching shear force is applied to the reinforcement steel buried in concrete, the projection of the head part engages with the concrete. Thus, it is possible to increase an anchoring force to the concrete.

Here, the anchoring force to the concrete can further be increased when the above-described reinforcement steel is deformed reinforcement steel provided with ribs on an outer peripheral surface of the shaft part.

Further, the reinforcement steel of the present invention is provided with a recess formed along a corner portion between the projection and an outer peripheral surface of the shaft part.

In this way, a stress is less likely to be concentrated on the corner portion between the projection and the outer peripheral surface of the shaft part when a tensile force in the axial direction is applied to the reinforcement steel buried in the concrete. Thus, it is possible to increase fatigue resistance at a junction between the head part and the shaft part.

In the case where the bottom surface of the recess is formed to be curved in the reinforcement steel in the present invention, a stress is less likely to be concentrated on the corner portion between the projection and the outer peripheral surface of the shaft part. Thus, it is possible to efficiently increase fatigue resistance at a junction between the head part and the shaft part.

The reinforcement steel of the present invention is capable of increasing the anchoring force to the concrete. The reinforcement steel of the present invention also allows to increase the fatigue resistance of the reinforcement steel since a stress is less likely to be concentrated on the corner portion between the projection and the outer peripheral surface of the shaft part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing reinforcement steel according to a first embodiment of the present invention.

FIG. 2A is a plan view, FIG. 2B is a side view, and FIG. 2C is a partial cross-sectional view showing the reinforcement steel according to the first embodiment of the present invention.

FIG. 3A is a front view and FIG. 3B is a rear view showing the reinforcement steel according to the first embodiment of the present invention.

FIG. 4 is a transverse sectional view showing a coupling structure using the reinforcement steel according to the first embodiment of the present invention.

FIG. 5A is a perspective view showing reinforcement steel according to a second embodiment of the present invention; and

FIG. 5B is a perspective view showing reinforcement steel according to a third embodiment of the present invention.

FIG. 6 is a transverse sectional view showing a coupling structure using the reinforcement steel according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

Note that in the description of the embodiments, the same constituents are denoted by the same reference numerals and overlapping explanations thereof will be omitted.

First Embodiment

As shown in FIG. 1, a reinforcement steel bar 1A of a first embodiment is deformed reinforcement steel made of steel. The reinforcement steel bar 1A includes a shaft part 10 and a head part 20 formed at a front end portion of the shaft part 10.

The shaft part 10 is formed by providing grid ribs 11 on an outer peripheral surface of a rod-shaped member having a circular cross section. Accordingly, the ribs 11 form asperities on the outer peripheral surface of the shaft part 10.

As shown in FIG. 2C, the head part 20 is formed at the front end portion of the shaft part 10. The head part 20 is a forged region of the front end portion of the shaft part 10. In other words, the shaft part 10 and the head part 20 constitute an integrated member.

An expanded-diameter part 12 having a diameter which is expanded from that in a region on a base end side is formed at an end portion on the head part 20 side of the shaft part 10. The expanded-diameter part 12 is a region of the shaft part 10 having the diameter being expanded by a pressure applied to a front end portion of the shaft part when forging the shaft part 10 to the head part 20.

In the first embodiment, an outer peripheral surface of the expanded-diameter part 12 is formed substantially at the same level as that of top surfaces of the ribs 11. Moreover, a maximum radius of the shaft part 10 is equal to a radius of the expanded-diameter part 12.

As shown in FIG. 1, the head part 20 is provided with: right and left projections 21 projecting from the outer peripheral surface of the shaft part 10 in a radial direction of the shaft part 10; upper and lower flat surfaces 22 extending parallel to an axial direction of the shaft part 10; and a front end surface 23.

As shown in FIG. 2A, the right and left projections 21 are regions that project in the right-left direction from the shaft part 10. In the first embodiment, amounts of projection of the right and left projections 21 from the outer peripheral surface of the shaft part 10 are substantially equal to each other. As shown in FIG. 3A, a side surface of each projection 21 is curved into a semicircular shape. As described above, the right and left projections 21 have substantially laterally symmetrical shapes in the first embodiment. However, the right and left projections 21 may have different shapes instead.

As shown in FIG. 2A, a base end surface 24 is formed at an end portion on the shaft part 10 side of each projection 21. The base end surface 24 is a flat surface that intersects with the axial direction of the shaft part 10. In the first embodiment, the outer peripheral surface of the shaft part 10 is located substantially perpendicular to the base end surface 24.

The front end surface 23 is formed at a front end portion of the head part 20. The front end surface 23 is a flat surface that intersects with the axial direction of the shaft part 10. In the first embodiment, the front end surface 23 is formed into a rectangle in front view as shown in FIG. 3A. Here, the shape of the front end surface 23 is not limited to a particular shape, and the front end surface 23 may be formed into an oval shape or a circular shape. Nonetheless, it is preferable to form the front end surface 23 into the rectangular shape so as to increase an axial cross-sectional area of the head part 20 and thus to increase shear strength thereof.

As shown in FIG. 2A, the head part 20 is formed such that the amounts of projection of the projections 21 are gradually reduced from the base end surface 24 to the front end surface 23. In the meantime, the right and left projections 21 form the substantially bilaterally symmetrical shape. That is to say, the head part 20 is formed to have the front end side smaller than the base end side, and into a substantially trapezoidal shape in plan view.

As shown in FIG. 1, the head part 20 is provided with an upper flat surface 22 and a lower flat surface 22. The upper and lower flat surfaces 22 are formed into the same shape which is a substantially trapezoidal shape.

As shown in FIG. 2B, the upper and lower flat surfaces 22 intersect with a direction (an up-down direction) which is orthogonal to the axial direction of the shaft part 10, and the upper and lower flat surfaces 22 are substantially parallel to each other.

In the reinforcement steel bar 1A of the first embodiment, a distance (a distance in the radial direction of the shaft part 10) from the shaft center (the axis) of the shaft part 10 to each flat surface 22 is the same as the radius of the expanded-diameter part 12. In other words, each flat surface 22 is not located outside of the outer peripheral surface of the shaft part 10.

Here, the distance in the radial direction of the shaft part 10 from the shaft center of the shaft part 10 to each flat surface 22 is set in a range from 100% to 115% of the maximum radius of the shaft part 10 (the radius of the expanded-diameter part 12). This makes it possible to hold the distance within a range of a manufacturing error when forging the head part 20.

Meanwhile, by setting the distance from the shaft center of the shaft part 10 to each flat surface 22 equal to or more than 100% of the maximum radius of the shaft part 10, it is possible to sufficiently secure the anchoring force of the head part 20 and to prevent the head part 20 from deterioration in strength.

In the meantime, by setting the distance from the shaft center of the shaft part 10 to each flat surface 22 equal to or less than 115% of the maximum radius of the shaft part 10, it is possible to prevent each flat surface 22 from being located largely outside of the outer peripheral surface of the shaft part 10.

As shown in FIG. 1, a recess 25 is formed along a corner portion between the base end surface 24 of each projection 21 and the outer peripheral surface of the shaft part 10.

Each recess 25 is a region of the base end surface 24 recessed along an outer peripheral edge portion of the shaft part 10. A bottom surface of the recess 25 is formed into a curved surface.

In the first embodiment, the recesses 25 are formed in the base end surfaces 24 at the time of forging the front end portion of the shaft part 10 to the head part 20.

Note that the method of forming the recesses 25 in the base end surfaces 24 is not limited to a particular method. However, when the recesses 25 are formed at the timing of forging, it is possible to retain the strength of the head part 20 because metallic fibers (fiber flows) of the head part 20 are not cut off in this case.

Next, a coupling structure for decks 110 by using the reinforcement steel bar 1A of the first embodiment will be described.

As shown in FIG. 4, the first embodiment will describe a coupling structure for coupling the decks 110 laid on a bridge superstructure 100 that includes RC decks.

The decks 110 that are adjacent to each other are placed on bridge beams with an interval in between. Thus, a space 200 is defined between the adjacent decks 110.

Each deck 110 is a precast member made of ferroconcrete. The reinforcement steel bar 1A of the first embodiment is laid inside the deck 110. Moreover, a region on the front end side of the reinforcement steel bar 1A projects in a horizontal direction from an end surface of the deck 110.

The upper flat surface 22 of the head part 20 of the reinforcement steel bar 1A is directed upward while the lower flat surface 22 of the head part 20 thereof directed downward.

Meanwhile, other reinforcement steel bars 2 are disposed between the reinforcement steel bar 1A projecting from one of the decks 110 and the reinforcement steel bar 1A projecting from the other deck 110.

After the reinforcement steel bars 1A are laid in the space 200 as described above, concrete C is placed in the space 200 to bury the reinforcement steel bars 1A in the concrete C.

Then, the reinforcement steel bars 1A in the decks 110 are anchored to the concrete C, whereby the adjacent decks 110 are coupled to each other through the intermediary of the concrete C.

In the above-described reinforcement steel bar 1A, when a tensile force in the axial direction is applied to the reinforcement steel bar 1A in the state of being buried in the concrete C, the projections 21 of the head part 20 as well as the ribs 11 on the shaft part 10 engage with the concrete C. Thus, it is possible to increase the anchoring force of the reinforcement steel bar 1A to the concrete C.

As shown in FIG. 1, in the head part 20 of the reinforcement steel bar 1A of the first embodiment, the recess 25 is formed along the corner portion between each projection 21 and the outer peripheral surface of the shaft part 10. Moreover, in the first embodiment, the bottom surface of each recess 25 is formed into the curved surface as shown in FIG. 2C.

Accordingly, in the reinforcement steel bar 1A of the first embodiment, when a stress attributable to a bending tensile force and to a punching shear force is applied to the reinforcement steel bar 1A as shown in FIG. 4, the stress is less likely to be concentrated on the corner portion between the projection 21 and the outer peripheral surface of the shaft part 10. Thus, it is possible to increase fatigue resistance at a junction between the head part 20 and the shaft part 10.

In the reinforcement steel bar 1A of the first embodiment, if one of the upper and lower flat surfaces 22 of the head part 20 is directed to an upper surface or a lower surface of the concrete C, then a covering depth T1 of the flat surface 22 of the head part 20 is subject to the regulation of a covering depth of the entire reinforcement steel bar 1A.

Moreover, the covering depth of the flat surface 22 of the head part 20 becomes substantially the same as a covering depth T2 of the shaft part 10. As a consequence, it is possible to control the covering depth of the entire reinforcement steel bar 1A, and thus to reduce the weight of the superstructure 100.

Although the first embodiment of the present invention has been described above, the present invention is not limited to the above-described first embodiment but can be changed as appropriate within the range not departing from the scope thereof.

In the reinforcement steel bar 1A of the first embodiment, the head part 20 is provided with the upper and lower flat surfaces 22 as shown in FIG. 1. However, the head part 20 may be provided with one flat surface 22 and the shape of the head part 20 is not limited to a particular shape.

In the first embodiment, each recess 25 is formed continuously into an arc shape along the outer peripheral surface of the shaft part 10 as shown in FIG. 3B. However, the width and depth of the recess 25 are not limited to particular values. Meanwhile, the recess 25 may be formed discontinuously instead.

In the meantime, the bottom surface of the recess 25 of the first embodiment is formed into the curved surface as shown in FIG. 2C. However, the shape of the recess 25 is not limited to a particular shape, and its cross section may be rectangular or triangular.

In the first embodiment, the ribs 11 are formed on the outer peripheral surface of the shaft part 10 as shown in FIG. 1. However, the ribs 11 need not be formed on the outer peripheral surface of the shaft part 10. That is to say, the shaft part 10 may be formed of a round rod.

While the first embodiment has described the structure for coupling the decks 110 to each other as shown in FIG. 3, the structure that can apply the reinforcement steel of the present invention is not limited thereto, and the present invention is applicable to various ferroconcrete structures.

In the first embodiment, the reinforcement steel bars 1A are laid in a direction of extension of the superstructure 100. Instead, the reinforcement steel bars 1A may be laid in a width direction of the superstructure 100 so as to connect decks that are juxtaposed in the width direction of the superstructure 100. Moreover, the layout structure of the reinforcement steel bars 1A including orientations, positions, and the like thereof are not limited. For example, the reinforcement steel bars 1 may be disposed below the other reinforcement steel bars 2.

Second Embodiment

Next, a reinforcement steel bar 1B of a second embodiment will be described.

As shown in FIG. 5A, the reinforcement steel bar 1B of the second embodiment has substantially the same configuration as that of the reinforcement steel bar 1A of the above-described first embodiment (see FIG. 1), except that the shapes of the head parts 20 are different from each other. In the reinforcement steel bar 1B of the second embodiment, the head part 20 is provided with a single flat surface 22.

Moreover, in the reinforcement steel bar 1B of the second embodiment, it is possible to control the covering depth of the concrete C by directing the flat surface 22 toward the corresponding one of the upper surface and the lower surface of the concrete C as shown in FIG. 6. In addition, the reinforcement steel bar 1B of the second embodiment has the larger projection 21. Thus, it is possible to increase the anchoring force of the reinforcement steel bar 1B to the concrete.

Furthermore, in the reinforcement steel bar 1B of the second embodiment, the projection 21 projects toward the inside of the concrete C (toward the other reinforcement steel bars 2). Accordingly, even if the reinforcement steel bar 1B moves inside the concrete C, it is possible to suppress a displacement of the reinforcement steel bar 1B by allowing the projection 21 to get stuck with the other reinforcement steel bars 2.

Although the second embodiment of the present invention has been described above, the present invention is not limited to the above-described second embodiment but can be changed as appropriate within the range not departing from the scope thereof as has been mentioned in regard to the first embodiment.

Third Embodiment

Next, a reinforcement steel bar 1C of a third embodiment will be described.

As shown in FIG. 5B, the reinforcement steel bar 1C of the third embodiment has substantially the same configuration as that of the reinforcement steel bar 1A, 1B of the above-described first and second embodiments (see FIG. 1 and FIG. 5A), except that the shapes of the head parts 20 are different from those of the first and second embodiments. In the reinforcement steel bar 1C of the third embodiment, the outer peripheral surface of the head part 20 is formed to be a circular shape.

In the reinforcement steel bar 1C of the third embodiment, the projection 21 is formed to be larger. Thus, it is possible to increase the anchoring force of the reinforcement steel bar 1C to the concrete.

Although the third embodiment of the present invention has been described above, the present invention is not limited to the above-described third embodiment but can be changed as appropriate within the range not departing from the scope thereof as has been mentioned in regard to the first and second embodiments. 

1. Reinforcement steel comprising: a shaft part; and a forged head part provided at an end portion of the shaft part, wherein the head part is provided with a projection projecting from the shaft part in a radial direction of the shaft part, and a recess formed along a corner portion between an outer peripheral surface of the shaft part and the projection, wherein a rib is formed on an outer peripheral surface of the shaft part.
 2. The reinforcement steel according to claim 1, wherein a bottom surface of the recess is formed to be curved. 3.-4. (canceled) 